I have seen many examples where a search task was launched from application but no examples where application could get some info back from that task.
For example, is it possible to get a list of found sites or URL that user have chosen in task (instead of navigating user to that URL)?
There is no built-in API in WP8 that would allow getting the results of a web search into your app. You should use a 3rd party framework for that.
Bing has an official Web API you can use for that but it starts costing money after 10,000 API calls per month. You can read more about it @ https://datamarket.azure.com/dataset/5BA839F1-12CE-4CCE-BF57-A49D98D29A44
Note that Bing did use to have a proper C# API with API keys and what not, but V2.0 of that API has been depercated in favour of the new Azure Data Marketplace service.
Google doesn’t have an API for search results. But for the past few years developers have used Google’s AJAX webservice to get those. See a C# code sample @ http://answers.oreilly.com/topic/2165-how-to-search-google-and-bing-in-c/